Need help with connecting sub to NAD325BEE

I tried hooking my HT sub to the 325. Plugged RCA into right and left in of the sub from the 325 preout. The music plays through the sub now and the speakers are in active. I can't find anything in the manual about setup. Obviously I'm doing something wrong. Can anyone explain the correct connections?

Do you plug the Y connectors in vertically or horizontally? I've been pluggin them in vertically in the Left and right configuration. The jumpers are in horizontally so maybe that is why I'm not getting sound from the speakers.